Infections and inflammatory stimuli cause an impairment of hepatic drug metabolism in humans and experimental animals, associated with decreases in the activities and levels of expression of many forms of cytochrome P450 (P450) in the liver. In humans, this can result in elevated plasma levels of therapeutic agents, and subsequent drug-related toxicity. These decreases in P450s may also be involved in the homeostasis and/or pathogenesis of the inflammatory response. The mechanisms by which these effects on P450 occur are poorly understood. Previous work in our laboratory has indicated that transcription of the rat P450 CYP2C11 gene is suppressed by cytokines via a binding site for the transcription factor NF-kappa. In the present project, we propose to define the role of this binding site in P450 suppression in vivo, and to elucidate the importance of additional cytokine regulatory sites on the CYP2C1 1 gene. We will also characterize the regulation of human CYP2C genes in cultured human hepatocytes. We will study the role of different hepatic cell types, cytokines and prostanoids in the suppression of P450 expression by bacterial lipopolysaccharide (endotoxin), using purified rat hepatocytes and hepatocyte-Kupffer cell co-cultures. Previous work in mice with a targeted deletion of the peroxisome proliferator-activated receptor-a suggested a role of this receptor in P450 suppression by inflammation. We will use cultured hepatocytes from these mice and wild type animals to determine the mechanisms responsible for the dependence on this receptor. Lastly, we will study the role of rat and human P450 enzymes in the inflammatory response itself, specifically in the generation of nitric oxide by hepatocytes stimulated with endotoxin or cytokines.